A pressure-sensitive recording material may comprise a combination of an upper sheet and a lower sheet. The upper sheet may comprise a support having a microcapsule layer provided thereon, the microcapsule layer containing microcapsules which are prepared by dissolving a substantially colorless color former in a suitable hydrophobic solvent, dispersing in a hydrophilic liquid to form micro-droplets, and encapsulating the resulting oil droplets. The lower sheet may comprise a support having a developer layer provided thereon, the developer layer containing an electron-accepting compound (hereinafter referred to as a "developer"). Alternatively, the recording material may comprise a combination of an upper and a lower sheet and an intermediate sheet comprising a support and a microcapsule layer provided on one side of the support and a developer layer provided on the other side of the support, or a material containing the above-described capsules and developer in the same surface thereof, or a material which contains a first layer comprising one of the above capsules and developer, and on which a second layer comprising the other is coated.
These pressure-sensitive recording materials are described in, for example, U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,730,457 and 3,418,250.
These pressure-sensitive recording sheets, however, have two disadvantages which are serious in practical use. First, the durability of the microcapsule layer containing the color former is not sufficiently high. Color-forming properties are reduced upon irradiation of the microcapsule layer with light. Second, the color-forming speed is slow, and the density just after printing is lower than that one day after printing.